1. Field of the Invention
The present invention generally relates to an assistant combustion agent used in a high-frequency combustion furnace for elemental analysis of carbon, sulfur or the like which are contained in a steel and iron sample, and a nonferrous metal sample.
2. Description of Related Art
A prior method of elemental analysis with a high-frequency combustion furnace has utilized a crucible made of ceramics housing a weighed amount of a steel and iron sample and a nonferrous metal sample. The samples are then heated by passing a high-frequency current through the samples and blowing oxygen gas at the same time to burn the samples. Subsequently, the combustion gas which is formed is transported by a carrier gas into an analyzer where the combustion gas is analyzed.
However, in the above described combustion, the samples cannot provide a sufficiently high combustion temperature (1,600.degree. to 1,800.degree. C.) and so carbon and sulfur are insufficiently extracted. Thus, in general, tungsten and tin have been used as an assistant combustion agent.
But, even the above described method using an assistant combustion agent has exhibited disadvantages. Tungsten is advantageous in that a specific resistance heat generated by the high-frequency current and a combustion heat are increased to promote an oxidation process. However, tungsten cannot cover all the sample where the sample is formed in a block-like shape or where the weight of the sample is relatively large. As a result, only portions of the sample brought into contact with tungsten are heated until high temperatures to burn out, whereby producing metallic films A, A and cavities B, B, as disclosed in FIG. 4, and the supply of the oxygen gas to these cavities B, B becomes insufficient to make the extraction of carbon and sulfur complete.
On the other hand, tin has exhibited a basic advantage in that a melting point and viscosity of the sample are reduced to satisfactorily bring the oxygen gas into contact all over the sample, whereby a satisfactory extraction can be achieved. However, a disadvantage has occurred in that tin cannot effect the generation of heat as does tungsten, whereby the analysis becomes difficult.
Accordingly, in order to satisfactorily burn the sample and carry out the complete extraction even in the case where the sample is formed in a block-like shape, or in the case where the weight of the sample is relatively large, a mixture comprising tungsten and tin at an appointed ratio has been used as an assistant combustion agent.
In the preparation of the mixture comprising tungsten and tin, those two elements have been separately weighed in the crucible and their mixture has been used as the assistant combustion agent. The assistant combustion agent has been put in the crucible together with the sample. However, the mixture has been inferior in uniformity, and the mixing process has taken much time, whereby the efficiency of the analytical operation itself is lowered.
To overcome at least some of the above problems, tungsten has been coated with tin or tin coated with tungsten to integrate tungsten with tin, as disclosed in Japanese Patent Laid-Open No. Sho 59-191671 and applied for by Horiba, Ltd. That method seeks to make the time required for mixing tungsten with tin in the analytical operation unnecessary and to carry out the analytical operation efficiently.
However, since tin is coated on a circumference of tungsten by immersing granular tungsten (having a particle diameter of, for example, 1.0 mm) in molten tin, when tungsten is integrated with tin by coating, a disadvantage has occurred in that a mixing ratio of tungsten and tin in the assistant combustion agent is apt to fluctuate.